Railroad cars in transit exhibit lateral roll due to track irregularities, inertia while negotiating turns, and even cross winds. Their high profile, high center of gravity, and great mass amplify these influences so that roll control is necessary to allow higher speeds around turns and to facilitate passenger comfort. Such lateral roll is exacerbated when rail cars are loaded with passengers or cargo, further increasing the car's mass and elevating its center of gravity.
In general, axles and wheels of a rail car are mounted on wheel trucks that in turn support a carriage. A two stage suspension system comprising a primary and a secondary stage is generally employed on the wheel trucks. The primary stage isolates the wheel truck, commonly referred to by those skilled in the art to which the present invention pertains as a bogie, from the wheels, while the secondary stage isolates the carriage itself from the bogie. The most common primary suspension systems employ wedges or chevron springs, typically made of rubber bonded to metal, and positioned between the bogie and the axles of the rail car. Primary suspension systems have little or no effect on controlling lateral roll.
In the above-referenced suspension system the carriage usually rests on a beam that spans the bogie parallel to the axles. This beam is referred to as a bolster by those skilled in the art to which the present invention pertains. The secondary suspension system includes mounts for coupling both the bolster to the bogie, and the carriage to the bolster. Generally, the bolster is supported on steel helical coil springs called bolster springs. The way in which the carriage is mounted to the bolster can vary. For example, a cleat and pad arrangement referred to as a side bearer mount is commonly employed. In this arrangement, the cleat is mounted to the bolster and can be in the form of a metal block or a block holding a wheel or a pad. Generally, the pad is made of laminated rubber and steel, and is bolted to the carriage underbody. More recent pad designs employ urethane springs bonded with rubber. These mounting devices physically limit the extent of rail car lateral roll but do little to dampen roll forces. Because these devices are not in continuous contact with the carriage, and because they employ little if any resilient material, these side bearer mounts do little to dampen impact between the carriage and the bolster during movement of the rail car. The high initial impulse of the carriage contacting the bolster can jar unsecured cargo within the carriage.
Secondary stage suspension systems for passenger carriages are generally more sophisticated than those for freight carriages, typically employing air suspension devices that may be used in conjunction with or in place of side bearer mounts. Air systems employ a rubber housing that defines an interior space filled with pressurized air from the rail car's pneumatic system. These air systems are mounted in pairs on either side of the bolster, at the center of the bolster, or both. They typically provide a smoother ride and better control of lateral roll than side bearer mounts. Some high speed trains employ computer controlled pressurized air suspension systems which further improves ride properties and lateral roll control. However, all of the existing air systems employ numerous interdependent components, making them expensive and prone to reliability problems. Recent innovations include using urethane springs bonded with rubber in the secondary stage suspension between the carriage and the bolster. However, the high compression forces generated during operation tends to degrade the bond between the disparate materials, leading to higher maintenance and replacement costs.
It is the general object of the present invention to provide a secondary suspension system that overcomes the drawbacks and difficulties associated with known prior art systems. It is a more specific object of the present invention to provide an economical and reliable device for use in a rail car secondary suspension system that assures a smooth ride for rail cars carrying passengers.